A warm, mostly dry start to spring and rapidly melting snowpack are expected to bring low streamflows across Western Colorado. 

“Going back into March, snowpack was near normal in the northern half of the state and below normal in the southern half of the state,” said Brian Domonkos, snow survey supervisor for the federal Natural Resources Conservation Services in Colorado, at the state’s May Water Conditions Monitoring Committee meeting… Fast forward one month… snowpack degraded relatively quickly.”

Statewide snowpack was at around 58% of normal on Tuesday, dropping from 93% of normal on March 24 as the snow melted faster and earlier than usual, Domonkos reported.

Snowpack typically peaks in late April in the northern mountains, he said. 

This year, snowpack peaked in the northern mountains just below normal. Statewide, it peaked at around 81% of the normal peak over the last 30 years, but it did so about 11 days earlier than normal, which impacts runoff efficiency, Domonkos said. 

“There are storms that come and add on to that snowpack later, but the majority of the snowpack in a given year has built up and is usually summed up for the most part in that snowpack peak,” Domonkos said. “That’s why I like to use it as an indicator of what runoff we should see…..that snowpack peak is usually about the maximum amount of volume from the snowpack that we’re going to see running off.” 

In March, when snowpack was near normal, “the majority of the state was expecting streamflow forecast to be near normal, at least in the northern and eastern portions of the state,” Domonkos added. 

“But unfortunately … snowpack has just been melting out a little bit too quickly, and precipitation has not been measuring up across the majority of the state, and so we’ve seen a decline across all basins over the last two months,” Domonkos said. “A below-normal snowpack peak as well as the early snowpack peak, and thus the early melt of snow will probably lead to drier streams at an earlier date than normal.” 

May’s streamflow forecasts from NRCS are well below normal across most of the state. Some of the northwest basins are closer to normal, including the Colorado River Headwaters, which was forecasted at 79% of normal streamflow volume. This is the highest in the state. Forecasts were the lowest in the southwest San Miguel-Delores-Animas-San Juan Basin at around 49% of normal. 

Despite the snowpack and streamflow picture, Colorado’s reservoir storage is sitting at 93% of normal. As of May 1, NRCS reported that Dillon Reservoir, Lake Granby, Blue Mesa and Pueblo Reservoirs were all holding near or above normal volumes. 

“Hopefully, with runoff pretty much in full swing at this point, we’ll see those reservoirs get to capacity,” Domonkos said. 

Domonkos added that if Colorado was to get “above normal precipitation during the melt period,” this would “boost streamflows and help the streamflow last longer.” 

However, the current and forecasted climate pictures are limiting the overall streamflow potential. 

“Based on what we’re seeing right now and future weather predictions, it looks like those streamflow forecasts will probably continue to decline,” Domonkos said.

A warmer, drier spring and water year

The first three months of spring were warmer and drier than average, following a string of warmer-than-normal months. 

“The first seven months of our water year (starting in October) were also among the top 10 warmest that we’ve seen on record,” said Allie Mazurek, Colorado Climate Center’s engagement climatologist, at the meeting. This accounts for the past 130 years since 1895. 

April itself was also warmer and drier than normal, despite a few “extreme temperature swings” including the snowstorm late in the month, Mazurek noted. 

“Notably, this has been our seventh straight drier-than-average April,” Mazurek said. “April is typically a pretty wet month in terms of snowfall, particularly across eastern Colorado, but lately, it has definitely been drier than average.”

With April being one of the state’s wetter months, Domonkos said precipitation would have needed to be significant to help Colorado’s broader water picture.  

“We really haven’t seen that as much as we would like to in those northwestern basins,” he added. 

Statewide, according to NRCS, April brought a 28% departure from the 30-year snow water equivalent baseline. Statewide precipitation was at 87% of normal last week, Domonkos reported. In April, statewide precipitation was 44% below normal.  

Similarly, while May has brought a few snow and precipitation events, it has done little to shift the overall picture for Colorado water and drought conditions. 

“We’re still running below average for this time of year in lots of these places,” Mazurek said. “We also saw some precipitation (last weekend) across the Western Slope, but the drought has been most significant there and it was not really enough to be drought-busting.”

The precipitation and cooler temperatures over the weekend did help the state hold onto snow a little longer, but it is unlikely to have any long-term impact. 

“In the northern half of the state, you can see the vast majority of the sites are below normal snowpack and just barely holding on to some of that snow, but it is melting off relatively quickly,” Domonkos said, referring to the SNOTEL (or snow telemetry) sites NRCS uses to track snowpack in the West.  

Snowpack levels were at 56% of normal as of May 21, at Rabbit Ears Pass according to the SNOTEL data.

Mazurek added that conditions in Western Colorado over the last month have “deteriorated in terms of drought,” only getting worse due to this lack of precipitation. The latest NOAA drought monitor released on May 15 shows much of the Western Slope in some kind of drought, with extreme drought developing in parts of Mesa, Delta and Montrose counties. 

These conditions are expected to continue. Mazurek, referencing the National Weather Service 8- to 14-day temperature and precipitation outlooks, said only “meager precipitation amounts are expected” in the form of “hit or miss afternoon thunderstorms.” 

Across the Western Slope, little to no precipitation is forecasted, Mazurek said, adding that this is less than normal. 

“That’s not great in terms of our drought expectations,” Mazurek said. 

However, Mazurek did note some uncertainty as different weather and climate models are predicting different precipitation amounts. 

“We’ll see how that shakes out… hopeful for rain for sure,” Mazurek said. 

No matter what May brings precipitation-wise, Domonkos said he “would bet that it might not make too much of an impact (on streamflow forecasts), seeing how quickly snowpack has fallen.”